Carbon dioxide (CO2) is colorless, odorless, non-flammable gas that we breathe in daily in small concentrations. The air we breathe contains about 0.03 – 0.04 percent, which is between 300 – 400 parts per million (PPM) of CO2.
Cannabis can use up to 0.12 – 0.15 percent (1,200 – 1,500 PPM) of carbon dioxide and this will make it grow up to 30% faster than under normal conditions. Carbon dioxide does not make more potent THC in cannabis, but it causes:
- More foliage grows in less time.
- Makes the plant grow more rapidly.
- Plants and leaves will be thicker.
- Slower to wilt.
Carbon dioxide affects plant morphology where parts of the plant will become denser, compact and less spindly allowing the plants’ flowers to grow more while the stems are able to bear the weight. There will be more development of flowers and sometimes flowers appear earlier when CO2 is used.
With rapid plant growth, they will need to be staked up so they do not fall over.
Another maintenance issue, when the air is enriched with carbon dioxide, is the plants will need more water and nutrients more often.
The water rises from plant roots and is released by the same stomata that absorb CO2 from the air during transpiration. CO2 enrichment causes plants’ stomata to partially close and this helps the plant to retain moisture in the form of water vapor.
This causes less water to be evaporated and thus can help lower humidity in a room. When rooms are enriched with carbon dioxide you will also need to have more air circulation and ventilation required due to heat and humidity.
Higher temperatures of 75 – 85° F (24 – 29° C) can be maintained when grow rooms are enriched with carbon dioxide; this stimulates a more rapid metabolism within plants.
Though, you should never let the room rise above 85° F (29° C) because at that point enrichment becomes ineffective and at 90° F (32° C) plant growth stops altogether.
Altogether, the most effective CO2 level is maintained at around 1,000 – 1,500 PPM throughout the entire grow room. When using CO2 be sure that your room is airtight, in addition to closing:
- Cover all outlets
- Light switches
- House air vents
- Any other hole with tape to seal them completely
Once this is done the ventilation system will be what brings air in-and-out of the room and this will help you to utilize all the CO2 most effectively rather than having it slip out of the room through holes.
Growers tend to use a 1:4 ratio of ventilation (Example: 100 CFM’s of air coming into the room and 400 CFM’s of air going out through ventilation) in a CO2 enriched room where it creates negative pressure so it better contains the CO2.
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